# Homework Help: How do I calculate the phase difference for this?

1. Apr 20, 2015

### Daniel Pinto

1. The problem statement, all variables and given/known data
Light with wavelength 100nm is incident perpendicularly from air on a film 0.500μm thick
and with refractive index 2.5. Part of the light is reflected from the first surface of the film,
and part enters the film and is reflected back at the second surface, where the film is again
in contact with air. What is the phase difference?

2. Relevant equations
phase difference = (2pi*deltaL)/lambda

3. The attempt at a solution
found the angle then added the vectors, used cosine rule and got an answer similar to it.

Last edited: Apr 20, 2015
2. Apr 21, 2015

### ehild

Welcome to PF!

Phase difference between what two things?

This is the phase change of a wave between two wavefronts delta L distance apart.

What angle did you find and what vectors did you add an why? And the answer was similar, to what? Show your work and result, please.